Spectrometers are a type of non-destructive testing instruments. They can be used, for example, to analyze chemical compositions and characteristics of substances. When light strikes a substance, according to the principle of light reflection and differences in the reflection, absorption or transmission of light of different frequencies due to compositions of substances, a spectrometer produces a spectrum after receiving light reflected from the substance. Given that different substances produce spectra of unique characteristics, the composition and characteristics of substances can be discerned accordingly.
FIG. 1 is a schematic diagram of a conventional spectrometer 500. Referring to FIG. 1, a beam of light enters into the spectrometer 500 and travels in free space towards a collimating lens 502. The light beam is then transformed by the collimating lens 502 into a paralleling light beam towards a grating 504. After being diffracted by the grating 504 and focused by a focusing lens 506, the light bam is directed towards a detector 508 which detects intensities of light of different wavelengths to produce a corresponding image. However, with the conventional spectrometer 500, due to numerous reflections, divergence of free space, and excessive light traveling path, significant divergence of light beams tends to result. Moreover, as it is difficult to clean conventional spectrometers to eliminate stray light therein, the existence of the stray light tends to cause excessive background noise in the corresponding image. Both of these drawbacks will affect the quality of the image produced by the detector 508, thus reducing the accuracy in the determination of intensities of light of different wavelengths by a post-stage circuit.